Nondestructive ultrasonic scanning or testing systems often utilize a coupling medium, typically a water mixture, discharged from a nozzle against the material or test object being scanned. The coupling medium in the form of a stream of fluid conducts ultrasonic waves to and from the material being scanned.
Laminar flow in the stream directed against the test object reduces backsplash generating noise and increases the signal to noise ratio as there is less signal attenuation and less noise and backscatter in the stream itself. Laminar flow also permits an increase in the throw distance, the distance between the nozzle and the test piece, that may be utilized without an unacceptable signal to noise ratio. Increased throw distance also facilitates improved ultrasonic testing, by way of example, by permitting streams to be properly directed against complex shaped test pieces, increasing testing speeds by providing more options for positioning of the streams and test equipment relative to the test object, and providing greater testing location accuracy as a result of less gravity induced drooping in the stream.
Streams may be directed at the test piece from one or more sides of the test piece, depending on the nature of the testing desired, such as reflective or transmissive ultrasonic testing. Laminar flow is also desirable in other applications beyond ultrasonic testing. Nozzles currently utilized in ultrasonic testing may employ porous media filters to generate laminar streams, as disclosed for example in U.S. Pat. No. 5,431,342 issued to Saripalli et al. The filters can require periodic cleaning. This results in undesirable down time for the testing equipment. Accordingly, there is an unmet need for nozzles providing for laminar flow without the use of porous media filters.